The effects of facilitatory and inhibitory kinesiotaping of Vastus Medialis on the activation and fatigue of superficial quadriceps muscles

This study aimed to investigate how facilitatory and inhibitory KT of the Vastus Medialis affected the activation and the fatigue indices of VM, Vastus Lateralis (VL) and Rectus Femoris (RF) throughout a dynamic fatigue protocol. Seventeen collegiate athletes (Ten males, seven females, age: 24.76 ± 3.99 years, height: 1.73 ± 0.10 m, mass: 68.11 ± 8.54 kg) voluntarily participated in four dynamic fatigue protocol sessions in which no-tape (control condition), inhibitory, facilitatory and sham KTs were applied to the Vastus Medialis in each session. The protocol included 100 dynamic maximum concentric knee extensions at 90°/s using an isokinetic dynamometry device. The knee extensor muscle activities were recorded using wireless surface electromyography. The average muscle activity (Root mean square) during the first three repetitions and the repetitions number of 51–100, respectively, were used to calculate the before and after exhaustion muscle activity. Furthermore, median frequency slope during all repetitions was reported as the fatigue rate of muscles during different KT conditions and for the control condition (no-tape). The results showed neither muscle activation (significance for the main effect of KT; VM = 0.82, VL = 0.72, RF = 0.19) nor fatigue rate (significance for the main effect of KT; VM = 0.11 VL = 0.71, RF = 0.53) of the superficial knee extensor muscles were affected in all four conditions. These findings suggest that the direction of KT cannot reduce, enhance muscle activity or cause changes in muscle exhaustion. Future studies should investigate the generalizability of current findings to other populations.


Methods
Participants. Seventeen physically active collegiate students (10 males, 7 females, age: 24.76 ± 3.99 years, height: 1.73 ± 0.10 m, body mass: 68.11 ± 8.54 kg) voluntarily participated in this study. They reported no history of surgery or musculoskeletal injuries such as muscle or ligament rupture, joint laxity, or bone fracture within the previous twelve months. Before participating, all subjects were briefed about the objectives and provided written informed consent, and all participants provided written informed consent prior to enrolment. This study was performed following the Helsinki declaration 33 , its later amendments and local ethics committee by the Research Ethics Committee of the Sport Science Research Institute (IR.SSRI.REC.1400.1010).
Instrumentation. An isokinetic dynamometer device (Biodex System 3, New York, USA) was used to measure the isokinetic concentric torque of the knee extensor. The EMG activity simultaneously was collected using 8-channel electromyography wireless (DataLITE, Biometrics Ltd, Gwent, UK) with a sampling rate of 2000 Hz during testing 34 . Bipolar active electrodes with a fixed centre-to-centre inter-electrode distance of 20 mm were used to record EMG signals.
Data collection. The measurements were obtained throughout four sessions (Fig. 1), with a one-week rest interval between each session. Each measurement session included five sequential phases: (1) Warm Up Before evaluating the measurements, all participants performed a general warm-up consisting of 5 min cycling (Biodex System 3 cycling ergometer) at 70 revolutions per minute (RPM) and 10 min of dynamic and static stretching for lower extremity muscles 35 23 . The tape was a waterproof KT (Ares, Korea, 5 cm wide and 0.05 cm thick). For the sham tape, two pieces of 15 cm × 5 cm tapes were applied horizontally above and below/under the muscle bulk ( Fig. 2) 26 . For the inhibitory taping, the KT was applied from the insertion to the origin, while the opposite direction was used in the facilitatory taping 8,41 . In both facilitatory and inhibitory modes, the percentage of tension was 50% its available (tape was first stretched to its 100% available tension and was marked by the ruler), and in the sham mode, there was no tension 42 .  110-degree angle. The participants practised at a submaximal contraction level to become accustomed to the equipment after placing the electrodes and warming up, and then they rested for a short while 38 . Next, they conducted 100 repeated isokinetic contractions utilizing the dominant leg knee extensors from 90 degrees of flexion to 0 degrees of flexion (full extension). The dynamometer was operated at a constant speed of 90°/s. While the arm of the dynamometer moved up from 90 to 0, subjects were instructed to perform maximally for each contraction across the entire range of motion (e.g., the contraction cycle's active phase). The subjects became relaxed when the dynamometer arm returned to 90 degrees (the passive phase of the contraction cycle). As a result, each contraction and relaxation period lasted one second, making two seconds for the contraction cycle. The 100 contractions were completed by all of the participants 38,43,44 .
EMG data collection and processing. We considered root mean square (RMS) and slope of median frequency (MDF), respectively, to quantify the muscular activity and fatigue rate, as these variables had commonly been used in previous studies 24,45,46 . The raw EMG signals were filtered using a zero-lag band-pass Butterworth filter at 20 and 400 Hz cut-off frequencies. Then, the root mean square (RMS, 50-ms windows) was calculated, and the muscle activity for each repetition was determined by calculating the mean of RMS values through knee extension (active phase) was normalized to MVIC 46 . To investigate the effects of KT in both pre and post-fatigue situations, the average muscular activity was assessed in three initial extensions and 51-100 repetitions, respectively 38 ; for this purpose, each cycle was separated from 90° flexion to 0° based on dynamometer angle data. Since the torque reduction in the fatigue protocol is considerably significant during the initial 40-60 contractions 43 , the average of the above repetitions has been considered as representing of pre-fatigue and post-fatigue conditions in the current research 38 . The values of the MDF were obtained using the short-time Fourier transform (STFT) technique for spectral analysis 45 . The STFT was obtained recursively (over 0.5 s timewindowed signals) using a 1024 point FFT (discrete and fast FT) with a rectangular processing window algorithm available in MATLAB® v.7.7. After applying the STFT, the MDF was obtained for further spectral analysis. The MDF, which is defined as the value of frequency that derives the EMG signal spectrum into two parts with equal energy, was calculated. Finally, the slope of the MDF was detected using linear regression between the MDF duration of the test (Fig. 3) 47 . The entire data analysis was conducted using MATLAB software (version 2020a, MathWorks, Inc., Natick, MA, USA).

Results
The descriptive results of the RF, VM, and VL muscles activity in the no-tape, sham, inhibitory and facilitatory conditions are reported in Table 1 Table 2). The findings of one-way repeated measure ANOVA and descriptive results of the MDF slopes of the RF, VM, and VL in the no-tape, sham, inhibitory and facilitatory conditions are reported in Table 3. According to these results, KT had no significant influence on muscular fatigue rate (MDF slopes) of RF (F = 0.73, p = 0.53), VL (F = 0.45, p = 0.71) and VM (F = 2.14, p = 0.11) ( Table 3).

Discussion
This study examined the effects of no-tape, sham, facilitatory and inhibitory KT of VM on superficial quadriceps muscle activity and fatigue. For muscular activity, the KT effect, the Time effect and the Interaction effect (Time × KT) were not significant. This data suggested no significant variations in muscle activity when various KT conditions were adopted, both in pre-fatigue and post-fatigue circumstances. For muscular fatigue, different types of KT techniques did not affect the fatigue ratio (MDF slope), neither for the VM with KT nor its agonist muscles, VL and RF.   www.nature.com/scientificreports/ Regarding the first hypothesis, the results showed that KT techniques did not affect muscle activation in the target muscle or its agonist muscles. In line with our findings, previous studies found no significant changes in muscle activation immediately following KT 14,21 . According to the present study and existing evidence, KT techniques do not affect muscle activity 14,21 , muscular fatigue and motor neuron excitability 48,49 , suggesting that KT techniques cannot influence the related parameter of muscle activation. However, the present study and previous research 21,43,44 have only involved healthy individuals; the effects of various methods of KT on muscular activation in patients with musculoskeletal pain have received less attention 8,14 . Another research on healthy participants found that KT had no effect on muscular activity among both regular KT users and non-users, while it positively affected strength improvement in regular users 17 . They suggested that placebo effects as an indirect mechanism could improve strength in regular users without influencing muscular activity 17 .
Based on time-frequency analyses, our findings portrayed that KT techniques had no effects on the fatigue ratio (MDF slope) for all superficial quadriceps muscles, thus rejecting our second hypothesis. We hypothesized that the KT would change muscle target fatigue and lead agonist muscles to change their activity to keep joint torque constant during a fixed task. However, the results indicated that the KT had no impact on the chosen muscle and that there is no cause for changes in the fatigue of its agonist muscles, as regards activation and fatigue rate of agonist muscles have not been influenced in the present study. To the best of our knowledge, only one study previously used the EMG fatigue index to evaluate KT effects 50 . This study inconsistently reported that KT effectively delayed Longissimus muscle fatigue (based on median frequency slope) in people with non-specific low back pain 50 . As low back pain individuals participated in their study, while the present study only recruited healthy adults, KT may have differently influenced muscular fatigue in patients. Regardless, we deliberately used a dynamic fatigue protocol in our study because it has been claimed that the KT mechanism is related to simulating muscle spindle and Golgi tendon organs 10 , and it is recognized that these proprioceptors are making feedback as responses to the changes of length and force during dynamic movements 51 . Moreover, Abubaker et al. reported that KT could significantly postpone muscular fatigue 18 . Since they measured the fatigue ratio based on joint torque changes, it is not clear which muscles are responsible for torque changes during fatigue protocol, and the KT's impacts may have been influenced by a lack of attention to the function of other muscles. The present study used EMG signals to evaluate the fatigue index separately for VM and its agonist muscles, VL and RF; however, we could not discover any evidence of KT's effects on muscular fatigue. Therefore, due to a limited number of studies and inadequate knowledge in this area, further studies are required to consider the suitable methodology, different types of muscle contraction and other muscles in the musculoskeletal system.

Limitations
In this study, some limitations should be acknowledged. First, since the participants of this study were healthy individuals, our findings could not be generalized to other populations of patients (e.g., presenting musculoskeletal disorders and pain or neurological injuries). Second, the results related to the joint torque (which is produced by all the knee extensor muscles) are not mentioned in the current study because the purpose was to evaluate the changes in the electrical activity of each surface quadriceps femoris muscle separately following KT applications. Finally, although a validated dynamic fatigue protocol 38 was applied, we did not directly measure using questionnaires different factors related to fatigue rate between measurements sessions, e.g., sleep quality 52 , mental fatigue 53 and nutrition diet 54 . However, none of the subjects reported sleep deprivation, malnutrition, or mental problems before the measurement sessions.

Conclusion
Based on the decrease of MDF (negative slope of MDF), the designed protocol resulted in overall muscular fatigue of quadriceps muscles. However, no statistical differences existed between no-tape, sham, inhibitory and facilitatory conditions on fatigue index, neither on taped muscle nor non-taped muscles as its agonist muscles. These findings provide preliminary evidence suggesting that KT may not be able to modulate muscle activity. Finally, there is limited research investigating the effects of KT on muscular fatigue, separately in all involved muscles. On the other hand, further research is required to obtain applicable information with a wide range of applications of KT in the treatment procedures.

Data availability
Data would be available on a reasonable request.